A number of types of implantable devices are in use to monitor and control the electrical activity of the heart. For example, it is known to have an implanted pacemaker interconnected via a transvenous pacing lead to an electrode in intimate contact with the myocardial tissue of the heart. The electrode can both sense the electrical activity of the heart and deliver an electrical stimulus provided by the pacemaker when required. Other systems include pacemakers and transvenous pacing leads which have a variety of sensor electrodes proximally spaced behind the tip electrode of the pacing lead. The sensors provide information to the pacemaker. There are also systems which monitor and provide automatic defibrillation utilizing an implanted power source and an electrode system, either attached to the surface of or implanted within the heart. Still other systems combine the pacemaker function with an automatic defibrillation capability, and may include multiple leads extending to internal as well as external portions of the heart.
More specifically, it is known to have a combination pacing, cardioversion, defibrillation and sensing lead implanted into the ventricle, and a large surface area patch electrode affixed to or near the exterior surface of the heart, both of which are connected to a pacemaker and/or a defibrillator. Additional pacing systems may also include a transvenous lead passively implanted into the coronary sinus, in addition to a lead which provides only sensing within the atrium. With this type of system, there may be three or more different pacing, cardioversion, defibrillation or sensor leads extending intravenously into the interior of the heart, in addition to a patch lead and electrode affixed to or near the epicardial surface of the heart, all connected to the pacemaker and/or defibrillator.
During the implantation procedure, the attending physician may implant a combination lead having pacing and sensing electrodes, which also includes a defibrillation electrode mounted proximally of the distal tip, and then test whether the defibrillation electrode can provide sufficient energy to defibrillate the heart. In the event that defibrillation requires too much energy or cannot be accomplished by the combination lead, a second lead may be implanted into the coronary sinus to act as either a cathode or anode for bipolar defibrillation and/or pacing or sensing between the coronary sinus lead and the combination transvenous lead placed in the right ventricle.
The physician may then determine the necessary electrical charge to defibrillate using the bipolar system, and determine whether or not a patch electrode must also be affixed to or near the epicardial surface of the heart or nearby, such as in a subcutaneous or subcostal site. If such a patch electrode is also required, following affixation of the patch electrode, the attending physician may test various bipolar combinations of the three leads for defibrillating the heart, using alternatively the patch electrode, the coronary sinus lead, and/or the electrode on the combination lead as the cathode(s) or anode(s) to determine the lowest threshold for defibrillation. Thus, while it may be necessary to have the patch electrode affixed to or near the exterior surface of the heart (or subcutaneously or subcostally near the heart), preferably if defibrillation can occur by the use of a combination pacing and defibrillation electrode placed in the right ventricle, and a coronary sinus electrode, the necessity for opening the chest cavity and affixing the patch electrode on or near the heart may be avoided.
When utilizing a coronary sinus lead electrode in conjunction with a pacing lead electrode to accomplish pacing, cardioversion or defibrillation, it is important to recognize that preserving the atrial-ventricle synchronization, by proper timing of the respective contractions, is very important to prevent the patient from adverse effects resulting from asynchronous contractions. Thus, in addition to providing the necessary pacing and defibrillation charges, it is extremely beneficial to have a system which can effectively preserve synchronization of the atrial and ventricle contractions by properly sensing the atrial depolarization and properly timing the electrical stimulus to the ventricle.
One method of obtaining the additional sensory information required to provide synchronization has been through the utilization of a separate atrial sensing lead, to provide sensing within the atrial cavity which provides additional information to the pacemaker. The atrial sensing lead may simply be implanted and allowed to freely float within the atrial cavity. Disadvantages of having a third intravenously implanted lead, include the fact that more hardware is implanted, perhaps to the detriment of cardiac function and optimal blood flow, in addition to the potential problems with its placement or implant location.
Accordingly, it would be very beneficial to provide a pacing system and cardioversion or defibrillation system which utilizes an improved coronary sinus lead electrode having the capability of being able to sense atrial electrical activity, thereby assisting the preservation of the atrial/ventricular synchronization while eliminating the need for an additional atrial sensing lead.